FHR1200 - Improved Shunt Regulator

The FHR1200 offers greatly expanded specifications versus that of the LM431. This includes: much wider operating temperature and voltage range, and the ability to directly drive a power supply controller unlike the LM431. Finally, the FHR1200 has much lower operating current for those applications where low Standby Power is important.

FHR1200 − Voltage Regulator »


  • Wide operating range: 7.5 volts to 120 volts
  • Low current operation: <10 µA
  • Full electronic temperature range: -55° to 150°C
  • The output can swing to ground.
  • Thermally stable operation
  • Flexible: The part can be used in many applications and configurations.
  • Fast slew rate: 1.5 MHz
  • Small package: SC-70-6 (SOT363)
  • Easy to setup: The output voltage is adjusted via the ratio of two resistors.

FHR1200 vs LM431

Operating Temperature0 ~ 70°C-55 ~ 150°C
Output Voltage Range2.5 ~ 36 V0 ~ 120 V
Regulated Voltage Range2.5 ~ 36 V7.5 ~ 120 V
Operating Current1mA ~ 100 mA10 µA ~ 50 mA
Application FlexibilityLowHigh
PackageSOT-23 (2.9 * 1.3)
SC70 (2.0 * 1.25)

The FHR1200 can operate down to currents as low as 10uA. This can result in significant power savings when compared to the LM431. The following figure illustrates this.

Comparing the Power Savings

Typical 24 V Output Regulator - Industry Standard LM431

Assumptions: (24 V Output LM431)
  1. LM431C requires 
    1 mA minimum bias current
    = 24 mW
  2. Voltage divider for LM431 often uses >1 mA
    = 24 mW
  3. Opto-Isolator (PC-817) requires average of 500 µA with FOD817c
    = 24 mW
    60.0 mW Total

Fairchild FHR1200

Assumptions: (24 V Output FHR1200)

  1. FHR1200: Requires 
    ~ 10 µA minimum bias
    = 0.24 mW
  2. FHR1200: Voltage divider requires 
    ~ 50 µA
    = 1.2 mW
  3. Opto-Isolator: Low current opto requires 42 µA (delivers 500 µA)
    = 1.0 mW
    2.44 mW Total

Another example of the power savings that can be realized with the FHR1200 is the following comparison of an LM431 output regulated supply versus a FHR1200 output regulated supply.

VCC Regulator for LCD TV Supply

192 W LCD TV Schematic of FSFR2100 Evaluation Board (LLC Resonant Converter)


The FHR1200 is very flexible. A simple discrete "Brown-Out" Regulator can be made using the FHR1200. The output regulator is also a FHR1200.

VCC Regulators & Voltage Ref for LED Supply


The FHR1200 is very flexible. A simple discrete "VCC Regulator," "Bias Regulator," and/or voltage "Reference" can be made.

As previously stated, the FHR1200 is very flexible so can be adapted to many different applications. The following illustration shows two ways the FHR1200 may be used to replace discrete components to regulate the input side of a LED offline power supply. On the left side, CV regulation is achieved two ways. First, a zener diode and BJT are used to sense the controller Vcc voltage, and to drive the feedback terminal of a controller chip. The Vcc voltage is used to represent the overall power supply output voltage. A problem with this is that regulating from the Vcc voltage requires an accurate voltage regulator. Using the FHR1200 rather than discrete components can significantly improve the regulator accuracy. Second, the Vcc voltage is used to feedback the error in the output voltage by driving the current limit pin on the controller. Once again this requires an accurate zener. Replacing the discrete zener with a programmable zener made up of the FHR1200 and two resistors can significantly improve accuracy.

LED Power Supply CV Regulation Improvement

Two ways to improve CV regulation with LED controllers using discrete parts | Improved CV regulation with FHR1200

Discretes Versus Integrated Solution

FHR1200 PinOut

So, why pay more for the FHR1200 versus discrete parts?

Improved Features Versus Discrete Parts:

  1. Thermally stable solution (around 50ppm depending upon how it is biased and on the temperature range over which it is operated.)
  2. Better accuracy (+/-2%)
  3. Wide temperature range (-55°C to 150°C)
  4. Very low operating current (<10 µA)
  5. Low cost
  6. Wide voltage range (0 to 120 V)
  7. Smaller footprint (SC-70-6), less PCB space