FM302E-I-type FM transmitter exciter is used in Japan NECs HPB a 1210 motherboard. Direct carrier frequency modulation, phase-locked frequency stabilization and frequency synth
esis. Preamplifier (BLF-177 FET) directly driven by an actuator, the maximum output power of 150W. Via the circulator to the last stage, as the final stage tube amp pushing stage. Pre-amplifier power supply with integrated power 4NICK48. Unfortunately, the present level no overvoltage protection circuit and DC voltage indication, so that the level sometimes happen that failure: actuator output normal, no power output at the same level, no final power output. The investigation is BLF177 amplifier tube breakdown burning ring, disconnect the power supply load, measured integrated 48V power supply output is 84V. Failure is part of the fault 4NICK48 integrated power regulator, 84V fault voltage amplifier tube BLF177 the breakdown burn again. Because of the power supply is fully sealed and can not be repaired. The integrated power amplifier tube and more expensive, the loss is very large. Therefore, it is necessary to present the power amp tubes plus over-voltage protection circuit, especially my station is located in the mountains above the summer thunderstorm season, often in series with the power line lightning, burned transmission equipment. Plus overvoltage protection circuit for safe, high quality broadcast off the air to reduce the rate, and save a lot of money. We use the library of existing components, design overvoltage protection circuit is shown, and install a terminal board, wiring simple, simple control, low cost, reliable experiments, very practical value. A copy of the protection circuit works described below, schematic diagram shown in Fig. FIG JX-based protection small box terminal board, fixed on the small box above, JX-1, JX-2 220V AC power connection; JX-3, JX-4 series with the transmitter control high voltage AC contactor block JC4 line package loop, this contact with the machine to control the high-pressure gear; JX-5, JX- * 8V voltage sampling. K-based small box work switch (OFF/ON). The switch in the protection circuit, as a reset switch, closing the re-closed. T for the input 220V, output 15V AC transformer. As the power supply of the device. Three-terminal power supply LM7812 + 12V DC output voltage. P 48V voltage for newly added instruction sheet (full scale 100V). V1 for the switching transistor (3DK9E), RB1, RB2, RW for the bias resistor (and sampling set circuit), RB1 13k. RB2 180 .RW 4.7k. J for small electromagnetic relay. Model: JRC-19F/012M.D5 protection diode (2CP20), D6 light emitting diode (red µ5mm), SSR for the exchange of solid state relays (model: JGX-2F). Protection control principle: RB1, RB2, RW sampling voltage divider circuit composed of 48V, when the power amplifier is normally + 48V, the adjustment potentiometer RW make V1 base voltage of 0.5V cutoff switch transistor V1, V1 collector to a high level. relay J does not pull its normally closed contact (4,6) is turned on to give a solid state relay SSR 12V input voltage and conduction, high-voltage AC contactor control block (~ 220V) JC4 pull, control high-pressure gear enter the normal working condition. When the 48V power amplifier exceeds 52V (this FET operating voltage of 48V. The maximum operating voltage is less than 52V, thereby protecting from the control voltage should be set to 52V). V1 switch group extremely 0.65V. This tube saturated conduction, the collector is low, the relay pull-J by J (4.8) normally open contacts self-protection (as 100W power amplifier controlled by a high-pressure gear. Block after block high voltage. The role is to protect themselves prevent 48V 100W power amplifier sampling circuit failure, causing relay alternately pass, off); J, electromagnetic relay normally closed contact (4,6) is disconnected, solid state relay SSR 12V input voltage cutoff lose, JC4 line package power release, blocking high-pressure gear. 100W power amplifier and then blocked, has protective effects. After identification and cause of the fault, the switch K closed off a little longer. The protection circuit is reset, the protection circuit into the next real-time protection status. Pretend after the first simulation protection experiments. Get a l: 1 The 220V isolation transformer and a voltage regulator. Assembled into a rectifier, filter power supply voltage output range between O-100V adjustable sampling voltage and analog 48V as 84V power supply failure, connect the protection circuit to test adjustment:. RW the sampling voltage at 48V, the relay J does not suck, normally closed contact (4,6) is turned on, AC solid state relay output series AC 220V25W incandescent bulb turned on shiny, high-voltage block simulation is working properly; when the sampling voltage is greater than 52V, the sampling voltage adjustment RW when 52V J pull the relay, normally closed contact (4,6) disconnect, AC solid state relay output is turned off, the incandescent light bulb goes off, the protection circuit simulation protection work. Then again change the regulator output: test J is working, through experiments and measurements can work as designed. The protection device on the machine to work. Up to now has been working for many years, the phenomenon has never been a malfunction of the pre-amplifier repeatedly play a protective role. The transmitter is connected with the overvoltage protection circuit: over-voltage protection circuit wiring board Jx-1, JX-2 AC 220V input connected, respectively, then the transmitter terminals X1-1, X2. JX-3 with JX-4 in series among JC4 line package line; JX-5, JX-6 were connected to the use of solid state power amplifier integrated power 4NICK48 positive and negative ends (that is, plug the transmitter connected XS4-14, XS4-12 feet), as 48V sample voltage. Voltmeter and JX-5, JX-6 terminals.