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Featured products - R1700 -

LED Driver IC with PFC and low EMI emission

June 1, 2018


Ricoh expands its portfolio of ICs targeted for LED lighting applications; the R1700 is a brand new product, powered directly from mains and converts its primary power source into a voltage suitable to drive LEDs. The IC is optimized for non-isolated LED driver circuits and has a wide input voltage range up to 650V to tolerate peaks in the supply voltage caused by switching inductive loads and to have enough safety margin. The PFC circuit improves the ratio between active and apparent power resulting in a lower load current from the source (electricity supplier).
We understood from the market that there is a demand for LED drivers addressing specific issues. Customers prefer to design a high efficient PFC circuit with synchronous rectification but are concerned about the EMI noise level caused by two switching MOSFETs.

The advanced R1700 has a Zero Voltage Switch (ZVS) circuit with Edge Resonance Control, which is able to reduce switching loss and EMI noise significantly by synchronous rectification. The image highlights the basic operation of the circuit more detailed.

A shows an ideal waveform of the voltage (Vds) and current (Id).

B shows the actual waveform of Vds and Id. When the MOSFETs turn on and off, switching losses occur due to voltage and current overlap.

C shows the improved waveform of Vds and Id using ZVS, any overlap between voltage and current are eliminated and minimizes switching loss.

Typically, faster switching operation generates high frequency noise that can lead to interfering system noise and other EMI issues; however, the R1700 can significantly reduce switching noise and EMI.

A conventional LED driver circuit usually consists of two switching DC/DC Converters whilst Ricoh's solution uses a unique one stage switching conversion with an advanced buck-boost (inverting) topology. Customers appreciate this advantage to skip one noisy switching circuit, reducing the number of bulky components on the board and save cost in this way.

Secondly, the edge resonance controlled Zero Voltage Switching (ZVS) circuit allows a high operating frequency and the use of small components. These two features makes the application suitable for integration in regular but also small and thin sized lighting fixtures. Compared to conventional circuits, a board-space reduction up to 70% and height reduction of 50% is achievable.

Conventional LED Driver Circuit

Conventional LED Driver Circuit / 2 Stage Switching Power Source

2 Stage Switching Power Source

R1700 LED Driver Circuit

R1700 LED Driver Circuit / 1 Stage Switching Power Source

1 Stage Switching Power Source

The R1700 has a LED brightness dimming range from 100% to 5% by connecting a PWM signal with a frequency from 1 to 10 kHz to the DIM input. As an alternative option, one could consider adding the R1580 constant current driver into the circuit. This IC converts a PWM signal into a linear dimming signal, the main advantages of this method is that the LED driver MOSFET is not continuously switching which supresses the harmonic current and EMI emission and results in a flicker-free LED operation. Especially when using the light source for recording photos and videos, the resulting footage quality will be lowered by flickering illumination. Striking effects are areas or lines on the footage with a different exposure. Another advantage of the R1580 is its wide dimming range; it extends the standard range from a minimum setting of 5% to 0.5%. In particular for RGB LED configurations, the extended dimming range ensures a wide control of the colour temperature settings. Below an example of the typical application circuit with the R1700 and R1580.

R1700 + R1580N Tupical Application Circuit, Buck-boost(Inverting)Converter

R1700 + R1580 Typical Application Circuit, Buck-boost (Inverting) Converter

We took care of the safety aspects as well, the R1700 has an array of protection circuits contributing to a safe operation of the application.

  • Overcurrent Protection (OCP)
  • Thermal Shutdown (TSD)
  • BST/VCC Pin Undervoltage Lockout (VCC UVLO)
  • VCC Pin Overvoltage Lockout (VCC OVLO)
  • Feedback Pin Overvoltage Protection (FB OVP)
  • CMP Pin Overvoltage Protection (CMB OVP)
  • Latch-Type Protection (optional by product version)
The latch circuit becomes active as soon the VCC OVLO, TSD or CMP OVP protection is triggered over 32 times and will stop the operation of the R1700. The latch version remains in this state until the circuit performs a reboot or when the chip is reset by using the DIM input pin. The non-latch version resumes operation automatically when the FB pin voltage returns to normal.