FM transmitter over-voltage protection circuit

FM302E-I-type FM transmitter exciter is the NEC Corporation, Japan's HPB with a 1210 motherboard. Direct frequency modulation of the carrier, using phase-locked frequency stabilization and frequency synthesis. The front power amplifier (BLF-177 FET) from the direct push actuator, the maximum output power of 150W. Through the circulator to the last stage as the final stage tube amp driving class. The front power amplifier power supply integrated with 4NICK48. Unfortunately, this level over-voltage protection circuit and DC voltage without instructions, so that sometimes happen in this level of failure: actuator output normal, no power output level, no power output of the final stage. The investigation is BLF177 amplifier tube breakdown burning ring, disconnect the power supply load, measured integrated 48V power supply output to 84V. Failure is part of the fault 4NICK48 integrated power regulator, 84V fault voltage amplifier tube BLF177 breakdown burn again. Because of the power supply is fully sealed and can not be repaired.

The integrated power supply and power amplifier tube prices are more expensive, the loss was enormous. Therefore it is necessary to 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. With over-voltage protection circuit broadcast on the safety and quality, reduce the rate off the air, a lot of savings.

We use the library of existing components, the design shown in the over-voltage protection circuit, and install a terminal board, wiring simple, simple control, low-cost, experimental work by reliable, very practical. A copy of the protection circuit works described below, schematic diagram, as shown.


JX-based protection plans in small box terminal board, fixed in the small box above, JX-1, JX-2 220V AC power connected; JX-3, JX-4 series with the transmitter in the control of high voltage AC contactor block Ⅱ JC4 line package loop, use this contact point to control the pressure of the machine Ⅱ block; JX-5, JX-* 8V voltage sampling. K-based small box work switch (OFF / ON). The switching action in the protection circuit when, as a reset switch, closing the re-closed. T for the input 220V, output 15V AC transformer. As the device power supply. LM7812 Three-terminal power supply output +12 V DC voltage. P 48V voltage for the additional instruction sheet (full scale 100V). V1 for the switching transistor (3DK9E), RB1, RB2, RW for the bias resistor (and sampling set circuit), RB1 = 13kΩ. RB2 = 180Ω. RW = 4.7kΩ. J for small electromagnetic relay. Model: JRC-19F/012M. D5 protection diode (2CP20), D6 light-emitting diode (red Φ5mm), SSR for the exchange of solid-state relays (model: JGX-2F).

Protection and Control Theory: RB1, RB2, RW sampling divider circuit composed of 48V, when the normal power supply +48 V amplifier, the adjustment potentiometer RW. So that the base voltage V1 0.5V. Closing switch transistor V1, V1 collector for high-potential, relay J does not pull its normally closed contact (4,6) connected by solid state relay SSR 12V input voltage and conduction, high-voltage AC contactor control block Ⅱ device (~ 220V) JC4 pull, control high pressure into the normal operation block Ⅱ. When the amplifier when the 48V power supply more than 52V (the voltage of FET 48V. Maximum operating voltage of not more than 52V, so the protection should also be set from the control voltage of 52V). V1 switch base is extremely 0.65V. This tube saturated conduction, the low collector potential, relay pull-J by J (4.8) normally open contacts self-protection (as 100W power amplifier controlled by the high pressure block Ⅱ. Block after block high voltage Ⅱ. The role of self-protection 48V 100W amplifier power is to prevent invalid sampling circuit, causing relay alternately pass, off); J, electromagnetic relay normally closed contact (4,6) is disconnected, loss of solid-state relay SSR 12V input voltage and cut-off, JC4 line package power release, blocking high-pressure Ⅱ gear. 100W power amplifier and then blocked, has protective effects. Failure to be identified and excluded, it will switch K closed off a little longer. Reset the protection circuit to protect the circuit into the next real-time protection status.

After loading into the first protection experiment simulation. To find a l: 1 the 220V isolation transformer and a voltage regulator. Assembled into a rectifier, filter power supply, voltage output range is adjustable between O-100V, as a sampling voltage and analog 84V 48V power failure, connect the protection circuit to experiment. Adjustment: RW to sample voltage 48V, the relay does not pull J, normally closed contact (4,6) connected to exchange solid-state relay outputs connected in series communication 220V25W incandescent bulbs turn the lights up, high-voltage block Ⅱ simulation is working properly; When the sampling voltage is greater than 52V to adjust RW so that when the sample voltage is 52V J pull relay, normally closed contact (4,6) disconnect, AC output solid state relay closed out incandescent bulbs, protection protection of the normal circuit simulation. And then repeatedly to change the voltage regulator output: test J is working, through experiments and measurements to work according to design requirements. The protection device on the machine work. Has worked for many years now, never malfunctions phenomenon, played several times before the power amp protection.

The over-voltage protection circuit and the transmitter connected: over-voltage protection circuit wiring boards Jx-1, JX-2 AC 220V input connected, respectively, then the transmitter terminals X1-1, X2. JX-3 with JX-4 in series JC4 line package circuits being; JX-5, JX-6 were called solid-state integrated power amplifier power supply with 4NICK48 positive and negative ends (that transmitter plugs XS4-14, XS4-12 feet), as the 48V sample voltage. Voltage header and in the JX-5, JX-6 terminals.


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