The author has perfected described previously in the journal of the wearable power supply radio ("Radio", 2002, No. 11, pp. 12, 13) by typing auto-switching power supply and battery. It should be borne in mind that umewaka power supply with such revision is appropriate only for equipment with sufficient headroom power speaker system.
As you know, currently popular wearable audio offline usually powered by built-in battery voltage 7.5 to 9...and In much less - 12 V. Almost all modern integrated USC used in wearable the equipment have a wide range of supply voltage and allow it increase to 14... 18 In [1]. Using this feature of ICS, often one only alteration BP network can be increased musical (peak) output power is more than twice [2]. Created instantaneous power supply improves the dynamic performance of the amplifier.
In the power supply of the radio [2] with a high for the unstabilized USC the voltage stabilizer is provided only to power a low power cascades device. The transition from mains to battery power mode was carried out push-button switch. With this switch and associated with a primary the disadvantage of the device: in case of accidental transfer button to "Battery" in the time from the network at the preliminary stages of the radio comes an increased stress, which can lead to failure of the universal amplifier and receiver.
This disadvantage is completely eliminated in the device which is schematically shown in the figure below. Here is the manual switch "Network-Battery" entered automatic electronic switching, excluding legal high voltage in the preliminary stages of the radio.
(click to enlarge)
In the "Battery" switch does not consume current; in the "Network" of its current consumption does not exceed 20 mA. Mode "Network" occurs when the voltage 11.5 V, and the transition into the "Battery" - V. 11
The switch is built into the existing radio power supply. Enter the allocated portion in the diagram a dash-dotted line. She is a sensitive and economical relay voltage and the integrated voltage regulator DA1. Unregulated voltage on the capacitor C1 keeps track field-effect transistor VT1. Transistor VT2 assembled a current limiter for the relay K1. Led HL1 indicates the switch to "Network".
When running on battery, when the voltage at the capacitor C1 even when fresh the batteries does not exceed 10 V, the transistor VT1 is closed positive the voltage on the gate that is set by the divider R1R2, below the threshold. Relay K1 de-energized, its contact To 1.1 is in upper circuit position. Stabilizer DA1 input disabled the contact K1.1, and the output - decoupling diode VD2, prevents battery discharge through the output resistance the stabilizer. In this state, the device consumes little current, which especially important in battery mode.
When network cable into the AC INPUT connector the battery is disconnected additional contact of the connector, and the voltage increases to the level of power USC. The voltage at the gate of the transistor VT1. Through the winding relay K1 will flow limited by the transistor VT2 current, but sufficient to the operation of the relay. The Contacts K1.1 will include in the supply chain stabilizer DA1. Now the voltage preliminary stages will be limited to the required level (9) and additionally stable. USC is powered by a heightened strain from BP, based on the recommendations in [2]. At the same time lights up the led HL1, indicate mode Network. When disconnecting the power cord is happening mode on battery.
Relay RES on the operating voltage of 12 V (passport 4.569.602 actuated when voltage 7...8 V and a current of 10... 12 mA. Without the limiter the current through the relay coil when the maximum supply voltage of USC 16 In its value would reach 35 mA, which is undesirable. To use relays for a voltage close to maximum, also not is the voltage is not stable and fluctuates with the work of USC. The application of the current stabilizer a field effect transistor VT2 limits the current consumption of the relay is higher than the trip current on 2...3 mA. This is sufficient for reliable switching and cost-effective conditions of instability of the supply voltage. High slope field transistor VT1 provided a small difference in the levels of switching around 0.5 V.
Diode avoids the use of one switching contact of the relay. Forward voltage drop on the diode VD2 (D - germanium) does not exceed 0.3 V and when using a silicon diode (CDA and similar) can be compensated by the selection circuits DA1. But with a germanium diode and without selection the accuracy of setting of the output voltage is sufficient and is 8.7±0,27 V.
The manufacture of the device should begin with the enhancement of the existing power supply. A typical transformer T1 in the radio, as a rule, low-power; it is better replace toroidal calculated at the effective voltage of the secondary winding, 1.2 1.3 times.. less allowable voltage specific chips USC. Some recommendations for choosing the annular magnetic circuit for transformer are given in [2].
Current consumption of USC after the alteration increases, so increase the capacitance of the filter capacitor to 4700 µf (25 V). High capacity filter also contributing to the increase in peak power and supply voltage to ensure reliable operation of the capacitor.
The input of the device is collected on a separate Board of appropriate size next to the main PSU. This device can also be used transistors KB, CPU, and in the position VT2 - KB or CPG (while sampling for the initial current flow - not less than 15 mA and KE). Relay K1 can be substituted with small with minimal operating current and a triggering unit, not more than 10 V. HL1 led can be replaced by another, but he must have sufficient brightness emit light when a current of 1...2mA. In order operational reliability of the chip DA1 and chip USC should be mounted on a small heatsink.
Establishing device is to install a trimming resistor R1 threshold voltage for switch "Network-Battery"; the current through the relay coil install the resistor R3. Before you configure the engines of the resistors R1, R3 should translate respectively into the top and left under the scheme provisions. Then using Latri gradually increase the voltage on the primary winding of the transformer T1, controlling the DC voltage on the capacitor C1. At the level of 11.5 In achieve opening of the transistor VT1 and the relay K1. The process visually noticeable by the LEDs HL1. The current in the relay coil control milliammeter and limit it at about 15 mA tuning resistor R3. After that, gradually reduce the primary voltage and check off: the relay K1 is released, visible on the extinction of the led HL1, must occur at a voltage of 11... 11.2 In the capacitor C1. On this the configuration is done.
BP electronic switching can be applied in various models wearable equipment. Reliability and ease of use is guaranteed by the absence of manual switches and power increase depends on the allowable voltage and limit the output power of USC.
Literature
Author: A. Pakhomov, G. Zernograd, Rostov region