Tri-M Systems HE104 - Manual (Page 17)

23 June 2005
HE104MAN-V8 Manual
Tri-M Engineering Tel: 800.665.5600, 604.945.9565
1407 Kebet Way, Unit 100 Fax: 604.945.9566
Port Coquitlam, BC V3C 6L3 E-mail: [email protected]
Canada Web site: www.tri-m.com
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CHAPTER 3: THEORY OF OPERATION
3.1 Input power protection
Input power is connected to the screw terminal block, CN1, which is removable from the socket
connector on the circuit board. A 10 ampere “pico” fuse F1 limits the current draw from the power
source. A series of devices, (toroid coil L3, transorb D4 and filter capacitors, C8A,C8B and C8D)
filters and clamps the input power.
Transorb D4 is a 5KVA, heavy-duty, transient suppressor. Transorb D4 provides “zener” type
protection and has an avalanche voltage of 43V. It is electrically located before fuse F1 to prevent
activation of the fuse during a “load dump” or large transient. Sustained voltages greater than the
avalanche voltage must not be applied or transorb D4 will fail.
3.2 Switching Regulator, +5VDC
A switching regulator IC1, generates the +5VDC output, which operates in a “buck” mode
synchronous switching regulator configuration. It does this by using inductor coil L1, upper mosfet
Q4, lower mosfet Q5, schottky diode D8, input filter capacitors C8A, C8B, C8C, C8D and output filter
capacitors C2, C3, C9A, C9B and C9C. Regulator IC1, is a current mode controller that adjusts the
“switching cycle” by the sensed current, instead of directly by the output voltage sensing error
amplifier, in regulator IC1. This further sets the current trip level. Operating frequency is set by
capacitor C5.
A total of 15 amperes can be supplied to the connected +5VDC load and +12VDC regulator, the –
5VDC, -12VDC charge pumps and the invertors. The +5VDC power is available on the PC/104
expansion bus and screw terminal connector CN2.
At start-up, a low dropout 4.5V source located in regulator IC1, provides the operating voltage Vcc for
the mosfets and control circuitry. After start-up, regulator IC1, is in a sleep mode whenever the
output level is within the burst mode voltage limits. As soon as the +5VDC output drops below the
burst low-level voltage, normal switching regulator operation begins and continues until the +5VDC
output reaches the upper burst level voltage. Then regulator IC1 is put into sleep mode again. When
low quiescent power mode is enabled, regulator IC1 burst mode operation will begin at approximately
1.5 ampere output. The output ripple when regulator IC1 is operating in burst mode, is 50millivolts.
The +5VDC regulator functions fully down to 6VDC input. Below 6VDC input, the +5VDC output will
track the input and have a drop proportional to the resistive losses on the HE104. The HE104
operates up to 40VDC input.